How to switch between two fonts using a decoding animation while the letters rain in from the sky
You can try per character animation using Decompose Text node. I think this node is much more flexible to use.
In this example i used falloff to offset size between two text instead of slicing.


For multiple text we can create text list. To appear each element once in a circular fashion we can use Shift List node. The setup below makes text element appea every 40 frame one by one.

Full node tree with a above setup added:


For back and forth effect we can create switches for matrices. Each switch will have two inputs reversed and non-reversed matrices list and output is altered using modulo function.